The demand for improved energy storage systems has increased greatly with the evolution of new equipment requiring new and improved battery systems as a power source. Critical characteristics that power sources must accommodate are low cost, high energy density, light weight, and good storability.
The present magnesium/manganese dioxide electrochemical system provides high energy density at low cost. It is similar in construction to the cylindrical zinc-carbon cell. That is, a magnesium alloy can, containing small amounts of aluminum and zinc, is used in place of the zinc can. The cathode includes an extruded mix of manganese dioxide, acetylene black for conductivity and moisture retention, barium chromate, and magnesium hydroxide. The electrolyte is an aqueous solution of magnesium perchlorate or magnesium bromide with lithium chromate. A carbon rod serves as the cathode current collector. The separator is an absorbent kraft paper as in the paper-lined zinc cell structure. Sealing of the magnesium cell is critical, as it must be tight to retain all moisture during storage but provide a means for the escape of hydrogen gas which forms as the result of the corrosion reaction during the discharge. This is accomplished by a mechanical vent--a small hole in the plastic top seal washer under the retainer ring which is deformed under pressure, releasing the excess gas. However, the present magnesium/manganese dioxide battery suffers great capacity loss of up to 66 percent during intermittent storage periods following partial usage. This reduction in operating capacity occurs because the moisture content of the cathode mix, which is very critical in the electrochemical reaction, is reduced as a result of the reaction: EQU Mg+2H.sub.2 O.fwdarw.Mg(OH).sub.2 +H.sub.2.